linux-kernel - [tip:x86/fpu] x86/fpu: Stop saving and restoring CR0.TS in fpu__init_check

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Date:   Tue, 1 Nov 2016 00:14:20 -0700
From:   tip-bot for Andy Lutomirski <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        brgerst@...il.com, torvalds@...ux-foundation.org,
        rusty@...tcorp.com.au, luto@...nel.org,
        dave.hansen@...ux.intel.com, mingo@...nel.org, hpa@...or.com,
        bp@...en8.de, peterz@...radead.org, dvlasenk@...hat.com,
        pbonzini@...hat.com, jpoimboe@...hat.com, kvm@...r.kernel.org,
        riel@...hat.com, quentin.casasnovas@...cle.com,
        fenghua.yu@...el.com, oleg@...hat.com
Subject: [tip:x86/fpu] x86/fpu: Stop saving and restoring CR0.TS in
 fpu__init_check_bugs()

Commit-ID:  fc560a80bac91e512fc37cdfe03a982ef4543c6b
Gitweb:     http://git.kernel.org/tip/fc560a80bac91e512fc37cdfe03a982ef4543c6b
Author:     Andy Lutomirski <luto@...nel.org>
AuthorDate: Mon, 31 Oct 2016 15:18:43 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 1 Nov 2016 07:47:53 +0100

x86/fpu: Stop saving and restoring CR0.TS in fpu__init_check_bugs()

fpu__init_check_bugs() runs long after the early FPU init, so CR0.TS
will be clear by the time it runs.  The save-and-restore dance would
have been unnecessary anyway, though, as kernel_fpu_begin() would
have been good enough.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@...cle.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Rusty Russell <rusty@...tcorp.com.au>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: kvm list <kvm@...r.kernel.org>
Link: http://lkml.kernel.org/r/76d1f1eacb5caead98197d1eb50ac6110ab20c6a.1477951965.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/fpu/bugs.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/arch/x86/kernel/fpu/bugs.c b/arch/x86/kernel/fpu/bugs.c
index aad34aa..d913047 100644
--- a/arch/x86/kernel/fpu/bugs.c
+++ b/arch/x86/kernel/fpu/bugs.c
@@ -23,17 +23,12 @@ static double __initdata y = 3145727.0;
  */
 void __init fpu__init_check_bugs(void)
 {
-	u32 cr0_saved;
 	s32 fdiv_bug;
 
 	/* kernel_fpu_begin/end() relies on patched alternative instructions. */
 	if (!boot_cpu_has(X86_FEATURE_FPU))
 		return;
 
-	/* We might have CR0::TS set already, clear it: */
-	cr0_saved = read_cr0();
-	write_cr0(cr0_saved & ~X86_CR0_TS);
-
 	kernel_fpu_begin();
 
 	/*
@@ -56,8 +51,6 @@ void __init fpu__init_check_bugs(void)
 
 	kernel_fpu_end();
 
-	write_cr0(cr0_saved);
-
 	if (fdiv_bug) {
 		set_cpu_bug(&boot_cpu_data, X86_BUG_FDIV);
 		pr_warn("Hmm, FPU with FDIV bug\n");